1. Technical Field
The present invention relates to a gearwheel intended for connection to a shaft through press fitting and to a shaft supporting a press fitted gearwheel. More particularly, the invention relates to a gearwheel, and a shaft supporting a gearwheel in which the press fitting is designed so that the average contact pressure in the press joint in a first area, situated radially within a cog path positioned on the gearwheel, is below the average contact pressure in an area situated outside that first area.
2. Background of the Invention
It is previously known, during manufacture of vehicle gearboxes, to utilize gearwheels that are connected to a shaft through press fitting. In this case, press fitting implies that the gearwheel has a central through-hole with a diameter smaller than that of the shaft to be inserted therein. In one assembly method, the gearwheel is forced into place, whereupon it is retained by the forces that arise due to the elastic deformation of the shaft and the gearwheel.
For example, the functional description of the Saab-Scania gearbox GRS900, Saab-Scania Division service (110) 1991, discloses a gearwheel equipped with a flange, which gearwheel is joined to a shaft in the gearbox through press fitting.
Press fitted gearwheels are used mainly when machining, construction, or economy does not allow the use of shafts with integrated gearwheels.
When a gearwheel is pressed onto a shaft in order to achieve a press joint, very large tensions arise in the gearwheel, as well as in the shaft. These tensions are a necessity to create a strong joint. In vehicle gearboxes, in particular in gearboxes for heavy vehicles, very large torques are transferred through the gearwheels included in the gearbox. In turn, this transferred torque gives rise to tensions, which are superimposed on the tensional field from the press fitting. The increased level of tension entails a risk for crack formation, in particular at the cog root, which leads to the possibility of a break due to fatigue.